1. Field
Aspects of embodiments according to the present invention relate to a pixel and an organic light emitting display device using the same.
2. Description of the Related Art
Recently, various thin and lightweight flat panel display devices (compared to cathode ray tube devices) have been developed. These include liquid crystal displays (LCDs), field emission displays (FEDs), plasma display panels (PDPs), and organic light emitting display devices. The organic light emitting display devices use organic light emitting diodes for emitting light when electrons and holes are re-combined, and have rapid response and low power consumption.
FIG. 1 is a circuit diagram illustrating a pixel of a conventional organic light emitting display device with NMOS transistors.
Referring to FIG. 1, a pixel 4 of a conventional organic light emitting display device includes an organic light emitting diode OLED and a pixel circuit 2. The pixel circuit 2 is connected to a data line Dm and a scan line Sn, and controls the organic light emitting diode OLED.
An anode electrode of the OLED is connected to the pixel circuit 2 and a cathode electrode of the OLED is connected to a second power source ELVSS. The OLED generates light of a particular brightness (e.g., a predetermined brightness) in response to current supplied from the pixel circuit 2.
The pixel circuit 2 controls the amount of current supplied to the OLED in response to a data signal. The data signal is supplied to the data line Dm when the scan signal is supplied to the scan line Sn. The pixel circuit 2 includes a second transistor M2 (that is, a driving transistor) connected between a first power source ELVDD and the OLED; a first transistor M1 connected between the second transistor M2 and the data line Dm, and driven by the scan line Sn; and a storage capacitor Cst connected between a gate electrode and a second electrode of the second transistor M2.
A gate electrode of the first transistor M1 is connected to the scan line Sn and a first electrode of the first transistor M1 is connected to the data line Dm. A second electrode of the first transistor M1 is connected to a first terminal of the storage capacitor Cst. Here, the first electrode is set to one of a source electrode and a drain electrode and the second electrode is set to the other electrode. For example, when the first electrode is set to a drain electrode, the second electrode is set to a source electrode. The first transistor M1 is connected to the data line Dm and is turned on when a scan signal is supplied from the scan line Sn. When turned on, the first transistor transfers a data signal from the data line Dm to the storage capacitor Cst. At this time, the storage capacitor Cst charges a voltage corresponding to the data signal.
The gate electrode of the second transistor M2 is connected to the first terminal of the storage capacitor Cst and a first electrode of the second transistor M2 is connected to the first power source ELVDD. The second electrode of the second transistor M2 is connected to a second terminal of the storage capacitor Cst and the anode electrode of the OLED. The second transistor M2 controls the amount of current flowing from the first power source ELVDD to the second power source ELVSS via the OLED in response to a voltage value stored in the storage capacitor Cst.
The first terminal of the storage capacitor Cst is connected to the gate electrode of the second transistor M2 and the second terminal of the storage capacitor Cst is connected to the anode electrode of the OLED. The storage capacitor Cst charges a voltage corresponding to the data signal.
The conventional pixel 4 displays an image of a particular brightness (e.g., a predetermined brightness) by supplying current corresponding to the voltage charged to the storage capacitor Cst to the OLED. However, the conventional organic light emitting display device cannot display an image of a uniform brightness due to a variation in threshold voltages of the second transistors M2 of the different pixels.
In a conventional organic light emitting display device, when different pixels have different threshold voltages of the second transistors M2, the respective pixels 4 generate light of different brightness in response to the same data signal. Thus, images of uniform brightness cannot be displayed.